Rotary piston pumps and motors of the circumferential piston type have potential advantages over reciprocating pumps due to the rotary motion of working members and near-continuous intake and outlet cycles. Potential advantages include: a compact size for a given output, decreased pulsation, reduced noise and vibration, relatively simple construction, and others. However, it has been impossible to achieve this potential in practice due to inefficient aspiration; poor heat dissipation; and problematic sealing and durability resulting in the need for extreme accuracy in machining and fitting the various parts. A review of the prior art illustrates these disadvantages.
U.S. Pat. No. 2,655,112 discloses a “Rotary Pump or Motor” whereby working fluid enters radially through the housing wall into a rotating interior chamber. The chambers rotation creates significant centrifugal forces that push fluid back out of the device and makes the required transit towards an inboard passage and thus into the working chamber inefficient. Within the working chamber itself, the rotor and gate have a conical profile that meshes when the two features are fully engaged. While this profile forms a seal at full engagement, it creates a significant gap at the points where the vane engages and disengages from the gate, thus decreasing efficiency. Another disadvantage of this device is that no device, apparatus or method are provided for cooling the interior rotating components. Gas compression applications generate significant heat which will transfer to the device, which in turn will transfer back to newly incoming gas media and potentially overheating the device. The sealing scheme on this device is also problematic. Eight seals are employed on the outer circumference of the working rotor plus an additional two on the vane tip. Increased frictional drag from ten large seals will erode much of the efficiency gained by eliminating leaks. Additionally, these seal points will wear and eventually fail, shortening the devices practical life. Another disadvantage of this device is accurately locating the two working components. They are located via bearings mounted on shafts, keyed into the rotors. The bearings are then journalled into an end plate, which is then attached via fasteners machined into the housing, which represents at least six points where machining and assembly accuracy are critical. From a practical standpoint, manufacturing this device would be difficult and costly.
U.S. Pat. No. 4,464,102 discloses some improvements to the above device but still with significant disadvantages. First, because of the outlet vents location on the housing wall, the vane will have no pumping action from engagement of the outlet vent until passing through the gate (roughly 25% of its rotation). During this period, no work will be accomplished and previously worked media will flow back into the working chamber. A check valve or other type valve isn't disclosed, but even with such a device installed, there will be backflow from any dead space between such a valve and the working chamber. Another disadvantage arises from the lack of an outlet port on the fore vane face. The intake port on the aft vane face efficiently deposits working fluid, but this fluid must then be forced around the circumference of the cylinder to the outlet passage thus creating turbulence, heat and inefficiency. Perhaps the more significant disadvantage is sealing between intake and outlet sides of the working surfaces. There is no active seal between the vane tip and the housing wall or the gate surface wall. Precise machining and assembly may reduce leakage but the costs to achieve this are prohibitive, not fully effective, and won't compensate for wear. Additionally sealing the tops and bottoms of the two rotor member from the endplates of the housing requires high precision and does not allow for wear. This device would be limited to low pressure applications. Another disadvantage, especially for a compressor or other gas application where heated media compounds inefficiency, is cooling of the rotor intake channel. Incoming working fluid will reside for some period in the rotor body and will carry some of the heat into the pump cylinder. Ideally this interior cavity would be actively cooled with minimal rise in working fluid temperature.
Ideally, a contemplated pump and/or motor should achieve the following goals: a) improve aspiration of worked media such that obstructions or hindrances are reduced and centrifugal force enhances flow rate, b) increase volumetric efficiency of the rotary stroke such that substantially the full volume of the cylinder cavity is utilized and converted to worked media each stroke, c) add active cooling to internal components in order to improve heat dissipation of the device and minimize ambient heating of working media, d) reduce design requirements for accuracy in manufacturing and assembly such that costs can be reduced and robustness added for improved durability, and e) accomplish the above goals while maintaining or improving advantages inherent in rotary cylinder devices relative to reciprocating pumps or motors, namely; compact size relative to work performed; efficiency (improved mass flow rate relative to work input); and quiet, low vibration, pulse-free operation. In addition, pumps and/or motors of simple construction should be provided that includes ease of assembly, low parts count, and manufacturability of components such that it can be produced at a competitive cost.